1. Field of the Invention
The present invention relates to a polishing liquid which is used for producing a semiconductor device, and in particular to a polishing liquid which is favorably used for polishing barrier metal materials for flattening in a wiring process of a semiconductor device.
2. Description of the Related Art
In the development of semiconductor devices such as semiconductor integrated circuits (referred to as LSIs hereinafter), higher density and higher integration by fine and laminated wiring lines have been required in recent years for miniaturization and high speed processing of the devices. One of various technologies used for this purpose is chemical mechanical polishing (referred to as CMP hereinafter). CMP is an essential technology for flattening the surface of a film to be processed such as an interlayer insulation film, for forming plugs and for forming embedded metal wiring, and is performed for smoothening a substrate, for removing excess metal thin films when forming wiring lines and for removing excess barrier layers on an insulation film.
In a usual method of CMP, a polishing pad is attached on a circular polishing platen, the surface of the polishing pad is impregnated with a polishing liquid, the surface of a substrate (wafer) is pressed onto the surface of the polishing pad, both the polishing platen and substrate are allowed to rotate while a predetermined pressure is applied at the back face of the substrate, and the surface of the substrate is flattened by a mechanical friction that is generated.
While fine wiring lines are formed in multilayer form for producing a semiconductor device such as an LSI, barrier metals such as Ta, TaN, Ti and TiN are formed in advance for preventing wiring materials from diffusing into the interlayer insulation films and for improving adhesiveness of the wiring materials when metal wiring lines such as Cu lines are formed in each layer.
In a conventional process for forming each wiring layer, CMP of metal films (referred to as metal film CMP hereinafter) for removing excess wiring materials heaped by plating is performed one or several times, and CMP for removing barrier metal materials (barrier metals) thus exposed on the surface (referred to as barrier metal CMP hereinafter) is subsequently performed. However, there are problems in that wiring portions are excessively polished by metal film CMP, which is called dishing, and further erosion is caused.
For reducing this dishing, in barrier metal CMP which is subsequently performed, it is required to adjust the polishing speed of the metal wiring portions and the polishing speed of the barrier metal portions, to thereby ultimately form wiring layers having fewer concavities due to dishing and erosion. In other words, since the wiring portions are rapidly polished to cause dishing and erosion when the polishing speeds of the barrier metal and interlayer insulation film are smaller than the polishing speed of the metal wiring material in barrier metal CMP, it is desirable that the barrier metal and insulation film layer have an appropriately higher polishing speed. This is not only because there is an advantage of enhancing the throughput of barrier metal CMP, but also because substantially dishing is often caused by metal film CMP and thus it is required to relatively enhance the polishing speeds of the barrier metal and insulation layer as mentioned above.
Various studies of polishing liquids have been made as follows.
While a CMP polishing agent and a polishing method for high speed polishing with little generation of scratches (for example Japanese Patent Application Laid-Open (JP-A) No. 2003-17446), a polishing composition and polishing method for improving cleanablity in CMP (JP-A No. 2003-142435), and a polishing composition for preventing polishing particles from aggregating (JP-A No. 2000-84832) have been proposed, it is necessary in the above-mentioned polishing liquids to appropriately control the ratio of the polishing speeds of the barrier metal layer and insulation film layer to the polishing speed of the metal wiring material, to thereby make the final concavities due to dishing and erosion as small as possible.